Astronomers have used careful observations of the motions of stars around the center of our Galaxy to make inferences about the mass of the object that lies at the center. They have concluded that these stars orbit a dark massive body, with a mass approximately 3 million times that of the Sun. The only known object that could be so massive and still be dark is a supermassive black hole.

The Milky Way galaxy's supermassive black hole, also known as Sagittarius A* (Sgr A*), is located in the center of this image (right). Chandra's observations have shown that flares from the black hole are very common. The cause of these flares is not understood, but they are thought to occur near the event horizon, or point of no return, around the black hole.